Population dynamics of two toluene degrading bacterial species in a contaminated stream

Toluene uptake by a benthic biofilm community was previously shown to vary seasonally from 0.03 m hr(-1) in winter to 0.2 m hr(-1) in summer in a solv ent-contaminated stream of the Aberjona watershed. We used quantitative PCR to estimate the population dynamics of previously isolated species of tolu ene-degrading Xanthobactcr autotrophicus and Myrobactetium sp. in both tolu ene-contaminated and uncontaminated reaches of the stream, and to estimate their relative roles in overall biodegradation rate. Quantification using s pecific 16S rDNA primers for X. autotrophicus and Mycobacterium sp. showed that populations of both species were much larger in the toluene-contaminat ed than the toluene-free reach, in agreement with earlier culture-based inv estigations. A relatively brief bloom of X. autotrophicus occurred in the c ontaminated reach in the summer, while Mycobacterium sp. populations occurr ed at elevated densities for more than 5 months. Calculations showed that M ycobacterium, previously thought to be less important than Xanthobacter in annual toluene degradation based on single time-point CFU estimates, appear s actually more important because of this longer persistence.